1. Field of the Invention
This invention is related in general to the field of pelletizing and briquetting of combustible materials. In particular, the invention concerns the use of liquefied biomass as a reactive binder for organic-waste material.
2. Description of the Related Art
Enormous quantities of wood waste material are produced both by recycling and as byproducts of industrial and commercial activity. For example, it is estimated that about 5,000 lumber mills in the U.S. continuously generate sawdust and wasted wood at a rate of approximately ten percent of the processed lumber. Similarly, over 1,100 cotton gins in the U.S. produce gin waste in the form of cotton stalks, mostly lignocellulose, which have to be plowed into the ground in order to minimize insect damage. The lignocellulosic stalks of corn, wheat, other grains, hays, grasses, sugar cane bagasse, and soybeans are also produced in large quantities but, with the exception of sugar cane bagasse, they are largely left to waste because of the expense involved in collecting them. Much potentially useful biomass is also available from dead wood in forests, which is typically destroyed by insects, microorganisms, or fires. Further, national forests have accumulated an excess of living biomass in the form of dense small trees, shrubs and pine needles that should be removed to save older, large trees from being destroyed in catastrophic wild forest fires. Moreover, solid waste from municipal sewage treatment plants consists of a sludge that contains organic material and toxic constituents that constitute a disposal problem. Similar wastes are produced by nearly 100,000 dairy operations in the U.S., which must continuously dispose of a mixture of bedding and manure, all organic material. Additional organic-waste material is produced in large quantities as waste from cattle, hog, chicken and turkey farms. Finally, it is estimated that approximately 280 million automotive tires are discarded annually in the U.S., ranging from 20 to 1,000 pounds in weight, which also represents a serious, continuing disposal problem.
Most of this waste material is currently being disposed of in landfills around the world. Approximately 300 million tons of solid waste is placed in about 3,500 landfills around the U.S. alone every year, about 70-80 percent of which is organic matter. Thus, it is clear that the magnitude of these organic wastes constitutes a serious environmental problem. As a result, increasingly stringent regulation of waste disposal practices are being imposed to satisfy environmental standards. Therefore, reutilization of these materials has become an important component of prudent industrial policy.
A related patent, U.S. Pat. No. 5,916,826, hereby incorporated by reference, describes a process for binding coal fines in briquettes based on the discovery that biomass liquefaction products are very reactive and can be used to bind active groups in waste-coal fines. That invention did not disclose a method for converting these additional sources of biomass waste material, such as from forests, lumber mills, dairies, cotton gins, farms, and municipal waste sludge, into combustible briquettes. The present invention is based on further work with liquefied biomass and the discovery that it can be used to produce useful, combustible agglomerates of waste material.
The primary goal of this invention is the use of liquefied biomass as a binder for agglomerating combustible waste material to produce a useful combustible product.
Another goal is the use of a liquefied biomass that is itself produced from waste material, thereby reducing the overall cost of the raw materials constituting the final product.
Still another goal of the invention is a binding process that takes advantage of the reactive nature of liquefied biomass material to produce a stable agglomerate in the form of a pelletized, briquetted, or molded product.
Finally, an objective of the invention is a binder that contains reactive groups which can be judiciously used to improve bonding with particular kinds of combustible waste material.
According to these and other objectives, the present invention consists of the combination of organic combustible waste material with a liquid binder produced by the direct liquefaction or fast pyrolysis of biomass material. Such liquefied biomass is produced according to known liquefaction processes in the absence of oxygen at typical temperatures between about 230 and 370xc2x0 C. (about 450-700xc2x0 F.) and typical pressures between 200 and 3,000 psi. Alternatively, a liquid biomass product may also be produced by the process of fast pyrolysis, which is instead carried out at atmospheric pressure and at temperatures of 400-600xc2x0 C. (about 205-315xc2x0 F.) with a residence time of about two to five seconds, or at temperatures greater than 600xc2x0 C. with residence times of less than 0.5 seconds.
If desired, the liquid biomass so produced by either direct liquefaction or fast pyrolysis may be mixed with additives (such as the heavy ends of fast pyrolysis, petroleum asphalts, natural bitumens, oils from tar sands, oils from shales, heavy ends of coal liquefaction, petroleum pitch, and petroleum coke derived from petroleum delayed coking processes) in order to modify its characteristics to meet specific needs of particular applications, and the resulting mixture is blended with the organic-waste material of choice. Depending on the nature of the waste material used, it may be advantageous to preheat it to enhance the binding reaction with the liquid biomass. While in some cases a preheating step up to 425xc2x0 C. (about 800xc2x0 F.) has been found to be advantageous, a preheat temperature in the 100 to 200xc2x0 C. range (250-400xc2x0 F.) is normally sufficiently beneficial for the purposes of the invention. Combustible extenders and fillers, reinforcing fibers, and cross-linking agents may also be mixed with the waste material prior to combination with the binder to provide additional specific properties to the mixture. The resulting well mixed mass may then be pelletized by the application of pressure or molded to a desired shape in conventional equipment.
Various other purposes and advantages of the invention will become clear from its description in the specification that follows and from the novel features particularly pointed out in the appended claims. Therefore, to the accomplishment of the objectives described above, this invention consists of the features hereinafter illustrated in the drawings, fully described in the detailed description of the preferred embodiments and particularly pointed out in the claims. However, such drawings and description disclose only some of the various ways in which the invention may be practiced.